Has the time come to stop changing the clocks? This is what the science tells us - The Guardian

I will admit that ever since I was a teenager I have been favourably disposed towards putting the clocks back in the autumn. The idea of an extra hour in bed after the clock has ticked back from 1.59am to 1am has always appealed to me.

What I have never enjoyed about the switch away from British summer time (BST) is that we lose an hour of daylight in the evening. That first Sunday afternoon when twilight arrives before 5pm is always a shock to the system. I can’t help but feel cheated. I know we get that hour of daylight back in the mornings, but somehow that earlier hour never feels like adequate compensation.

For me, losing the evening light marks the end of runs in the fields away from the glare of the streetlights and the noise of traffic, and the end of the kids playing out on the street after tea. In some sense it feels like the start of a less sociable winter “hibernation” period. This melancholic time, in which the early darkness is brought on abruptly, has even been linked to seasonal depression.

The argument in favour of our autumnal reversion to Greenwich Mean Time (GMT) is largely based on its effect on mornings. It ensures that most people who work nine to five in the UK will arrive at work in daylight. For example, even up in Edinburgh (more than 93% of the UK population lives below the city’s latitude) official daylight never arrives later than 8.45am, even in the depths of winter.

Opponents of our biannual time switch point out that it is at best confusing and at worst bad for our health. But what does the research tell us? Several studies have shown that the first weekdays after the clocks go forward in spring are associated with an increase in heart attacks of up to 24%. It should be noted, however, that the weekdays that follow the clocks going back see a roughly commensurate fall, and overall the numbers are unaffected by daylight saving transitions. These changes in heart attack incidence are thought to be linked to the impact of sleep on cardiovascular health. The transitions between GMT and BST (and vice versa) have been shown to disrupt sleep and circadian rhythms in some people for weeks after they take place. The impact of the switch has even been linked to increases in fatal traffic accidents.

So it seems that this annual switching may be a suboptimal strategy, as the statistics suggest that the changing of the clocks has a demonstrable impact on our health. But if we are to stick with one time system all year round, which should it be: the lighter mornings of GMT or the lighter evenings of BST?

In favour of year round GMT is the fact that morning light is thought to help wake us up and to improve alertness. The American Medical Association has also argued that standard time (US winter time), in which noon occurs at the point when the sun is highest in the sky and thus means lighter mornings, aligns best with human circadian biology. Additionally, exposure to light later in the day, as experienced during BST, is believed to delay the body’s release of melatonin – a hormone which, among other functions, helps us feel drowsy. The consequence is that on days with lighter evenings, which we may enjoy for the greater leisure time they provide us, we tend to sleep less overall. And it’s well established that too little sleep has all sorts of detrimental health effects, from decreasing our learning capacity to elevating the activity of genes associated with inflammation, stress, heart disease and diabetes.

On the other side are the arguments that underpinned the original introduction of BST. During the first world war, Germany and then the allies introduced daylight saving time as a way of saving energy, reasoning that increased light in the evening would reduce the consumption of energy. More recent studies have, however, suggested that our modern power consumption habits mean energy savings made by reducing evening lighting are now often offset by increased energy consumption, for example through our use of air conditioning or the increase in travel to leisure activities in the warmer, lighter evenings.

But there is evidence to show BST can have a positive impact on our health as well. When it is lighter in the evenings, studies suggest we spend more time outside taking exercise or on other recreational activities, and less time engaged in sedentary indoor activities such as watching TV. An early BST proponent, Winston Churchill, opined that it enlarges “the opportunities for the pursuit of health and happiness among the millions of people who live in this country”. There’s also a strong argument that the lighter evenings BST affords make our lives safer. One study in the US suggested that year round daylight saving could reduce pedestrian fatalities by 13% and motor vehicle fatalities by 3%. Other studies have shown that longer daylight hours lead to a reduction in crime.

If forced to choose, a recent YouGov poll found, 59% of Britons would opt for the lighter evenings of year round BST, while only 22% would be in favour of continual GMT. However, it seems we are less decisive about whether we should abolish the current daylight saving time switches, with 39% wanting to scrap the process and 44% in favour of the status quo. And while in 2019 the European parliament voted to scrap mandatory daylight saving, it looks unlikely that we in Brexit Britain will be considering that option any time soon – however much we pine for the light.

• Kit Yates is director of the Centre for Mathematical Biology at the University of Bath and author of The Maths of Life and Death

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Has the time come to stop changing the clocks? This is what the science tells us - The Guardian
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